Just to be clear the NFL was around much longer than the Superbowl, so to say Superbowl winners since the start of the NFL is weird. Maybe reword it to say since the start of the Superbowl Era.
Agree. The NFL was formed in 1920 as the American Professional Football Association (APFA) before renaming itself the National Football League for the 1923 season.
You beat me to it. Also, I'd recommend reformatting the quiz so that people must name the champions by year, and the answer would have to correspond with the yellow box, like the NBA and MLB champions quizzes. Considering Super Bowl Sunday is right around the corner, you would have a pretty decent chance of being featured.